1. Field of the Invention
The present invention relates to an exhaust pipe.
2. Discussion of the Background
In order to treat injurious substances such as injurious gases contained in exhaust gases discharged from an engine, a catalyst converter is installed in an exhaust gas passage including an exhaust pipe.
In order to improve the conversion efficiency of injurious substances by the catalyst converter, it is necessary to maintain the temperature of exhaust gases and the temperature of the exhaust pipe and the like through which the exhaust gases is allowed to pass at temperatures suitable for activating the catalyst (hereinafter, referred to also as a catalyst activating temperature).
However, at the time of high speed operation of the engine, the exhaust gas temporarily has such a high temperature as to exceed 1000° C. Therefore, the temperature of the exhaust gases sometimes becomes higher than the upper limit value of the catalyst activating temperature. As a result, problematically, efficient purification of exhaust gases may be difficult and the catalyst may deteriorate.
For this reason, an exhaust pipe connected to an automobile engine needs to be capable of externally radiating heat of the exhaust gases passing through the exhaust pipe at the time of high speed operation of the automobile engine.
JP-A 2009-133213 and JP-A 2009-133214 have disclosed an exhaust pipe having a structure in which a layer composed of a crystalline inorganic material and an amorphous inorganic material is formed on a surface of a cylindrical base material made of a metal.
JP-A 2009-133213 has disclosed an exhaust pipe having a structure in which a layer composed of a crystalline inorganic material and an amorphous inorganic material has infrared-ray emissivity higher than that of the base material so as to provide the exhaust pipe with an excellent heat releasing characteristic.
Moreover, JP-A 2009-133214 has disclosed an exhaust pipe having a structure in which the amorphous inorganic material located on the outer peripheral side from the crystalline inorganic material has an average thickness of 20 μm or less so as to provide the exhaust pipe with an excellent heat releasing characteristic.
The contents of JP-A 2009-133213 and JP-A 2009-133214 are incorporated herein by reference in their entirety.